JLH 10 Watt class A amplifier

[nigel pearson]

The best bass I ever had was my baffle speakers. I have a nothing special photo if I can find it. If you did the maths like a bumble bee it won't fly. 15 inch bass Qts 1 2 12 inch full range Qts 0.95. Efficiency circa 98 dB/watt. Eq was considerable to get bass balance. Frequency response 40 Hz .3dB and 30 Hz -15 dB. Typical non distorted levels 115 dB. The bass was addictive. The sound had its own coloration which I mostly eliminated with a super tweeter. The amplifier a slightly modified Quad 303. A friend visiting the house said it to be a £20 000 sound or better. It was as unlikely as a jumbo jet doing loop the loop. I understand they can do barrel rolls!

I am listening to my Sony radio tuner circa 1973. It's a nostalgic sound. I suspect it has 50uS deemphasis instead of 75uS. Maybe a project. I made a 1.5 metre dipole for it out of scrap copper pipe. It's sublime. BBC radio 3 French impressionist piano. Image. My favourite La Cathedral Engloute if you pardon French dyslexia. I feel that means the engulfed cathedral. The sound of the bells under the water.

I am yet to visit India. Sri Lanka was beautiful. I went by train. A Hitachi locomotive rebuilt in the UK! 5 foot 6 width. The Empire got better than us. 4 foot 8 1/2. inch is Roman. I have a photograph in France of chariot grooves. Exactly the same size. At St Cristol near Lunel.

 

[jemraid]

Hmmmm clipping

9:55 PM Sensing elements
YouTube

A wall of full frequency sound, beware, this is not 'play my dirge'

This
4K Video Downloader | Free Video Downloader for PС, macOS and Linux | 4K Download
plus this
Audacity (R) | Free, open source, cross-platform audio software for multi-track recording and editing.
will see it onto a cd

Cheers

 

[Ian Finch]

For radio listening Nigel, get yourself a decent old tuner like the Pioneer F9 or F90. The difference of an unusual pulse counting FM detector in these is like night and day among the older synthesized tuner designs of the 1980s and Pioneer did it so well, even back then. I have read some reviews that don't give these as great a rating as I think they deserve but then, I haven't auditioned everything under the sun either.

 

[nigel pearson]

I think my baffles would have suited the JLH and use the 303 for the bass alone. I could fashion the bass exactly a I want. The way most people get bass nothing like this. 1950s sound. Natural roll-off or boost.

The point I didn't make is being very efficient distortion was very low. The cones seldom moved even though my neighborhood must have heard them. Very tight and very fast. Each note a note. I would have liked an extra octave, 30 Hz was possible. The baffles Ply MDF composite.

My best wishes to everyone also. Now to make some soup. Leeks to start.

 

[Ian Finch]

I don't follow your argument there. If speakers are efficient, it means the cones move more than those of less efficient but comparable sized speakers. If you mean that bigger cones make more sound than small ones, you aren't talking about efficiency any more because the issue is now one of air displacement and you still need about the same amount of power to reach a certain SPL with relatively small or large cones.

 

[nigel pearson]

The comparable distortion is caused by a coil starting to leave the magnetic field. This is classic cause of second harmonic distortion. The flux density being reduced. Simple valve amps have similar distortion as heading to the anode is different to trying to reach the cathode. Specifically one wave side is bloated. If a speaker is more efficient the movement from the coil gap is lower. Certainly cone area helps. Qts often quoted isn't the whole story. Some speakers move more than others when ideally they shouldn't. My own seemed to play warped records without problem. We have been brought up thinking new is always best. Speakers that can work without amplifier damping have advantages. Due to science used they can even compete with modern designs. Some use carbon fibre as part of the paper.

 

[thoglette]

.. same amount of power to reach a certain SPL with relatively small or large cones.

Not quite: two things are going on here
1. same amount of acoustic power. Most of our power-delivered-to-the-speaker is not translated into acoustic power. Efficienct speakers/boxes convert more of the delivered power (up to 100x more e.g. 86db/W vs 107db/W) into sound.

2. all other things being equal, the bigger cone moves less. And, all other things being equal, the cone that moves less distorts less.

2b) all other things being equal, the better coupled cone moves less (see horns).

Dipoles couple differently to boxes, especially once the wavelengths get up and the dipole size is of the same order as the room dimensions. They also don't suffer "boxiness" as badly (panel vibrations are near zero and the only reflections are from the wall behind).

 

[Hiten]

Clipping produces momentary bursts of a wide range of harmonics of whatever audio frequencies you feed it with - even bursts of DC can be seen on an oscilloscope. The only reduction of clipping distortion will be if the level of any audio input you feed it with is amplified only to a level that is below the clipping threshold and that is related to power ratings, supply rail voltages and amplification factors.

However, its safe to assume that most forms of classical and pop music have much greater bass content and hence smaller amplifiers with lower clipping thresholds can be used for treble speakers. It's common in posts here to read of someone taking advice to build 100W active crossover speakers but use only 10-20W treble anplification and that's where the JLH and similar class A designs come in. Otherwise, you can't reduce clipping levels by filtering frequencies alone.

Thanks. So I suppose three way active system with 2 separate Class A amps for mid and high and more powerfull amp for sub/woofer would be appropriate if one wants class A system. May be a separate thread required. Thanks all for inputs.
Regards,

 

[Ian Finch]

Re: #6147,8
Quite so. As you add to the argument, all other things should be considered equal. I should have included more conditions too but that would have meant turning the query into a rave that I'm not prepared for.

Distortion was certainly a consideration in Nigel's post but it was linked to efficiency, something that in my experience is usually the reverse, where efficient speakers (say, PA type) typically have worse distortion than those designed for hifi where long gaps, coils and suspensions became essential for bass linearity, as AR's Edgar Villchur demonstrated long ago.

In a simple model, compare the displacement of a single 350mm cone against 2 x 300mm cones delivering the same total SPL. That is a common alternative for PA and instrument speaker arrays where the economy of a single bass driver can outweigh the other benefits of compact multi-arrays. Axially, the 300 mm cones will now move less than the 350mm cone for the same total SPL, all other things being equal, no? So, why not expect lower distortion from the smaller cones?

 

[thoglette]

something that in my experience is usually the reverse, where efficient speakers (say, PA type) typically have worse distortion than those designed for hifi

Agreed, if all other things are equal (e.g. budget, including shipping) efficiency and fidelity can be traded off.

And the main stream has been allergic to trading off maximum power dissipation because, you know, it's a number you can sell.

That, by definition, the average person in this thread only has 10W to expend doesn't even figure on the radar.

Now, I've recently obtained some exceedingly heavy, reasonably efficient, well regarded (w.r.t. various forms of icky behaviour) drivers which can put up with 4db more power that the JLH puts out. But they're of a similar vintage as myself - there's not much like that on the market today.

 

[nigel pearson]

Robin Marshall ex of BBC research inspired my speakers. Pano a moderator here added to it. My first experiments were with conventional drive units and showed that they were hopeless. Sound was glorious but unable to deal with cutting lathe rumble for example. Big paper cone drive units cope very well and show virtually no movement producing surprisingly deep bass. Organ music especially powerful. If you can't hear and feel cutting lathe rumble on 1920s 78s the speakers are not working. Like rock concerts it's unpleasant when the music stops and hum is heard. It is wonderful to hear the room on a 78 with the piano in the background. Very quickly you are almost there and the lack of frequency range is not so obvious. Robin's point to me was that the sound of the Quad electrostatics was not much to do with being electrostatic. He also said magnetic circuits can not be infinitely scaled up unlike amplifiers. Thus higher efficiency is desirable.

The extreme opposite was AR3. Given enough watts they could do a very good job.

 

[nigel pearson]

One thing I forgot. These pa drive units are unrecognisable on a baffle. Once resonances dealt with they are so damn fast and open. I drapped a sheet over the backs. Disaster.

I wish I had measured the thd. It seemed low. It might be that unlike most things it wasn't compressed. My friend John says a pa rig is the best sound you will ever hear if at domestic levels and balance set to suit. In that mode other filter curves can be used that are not typical of pa. He does classic music using pa. His home speakers Meridian active.

 

[nigel pearson]

Just before moving house. 4 foot high. 15, 12 inch drives.

 

[jemraid]

Hello all,

In order to make notes on what components I am going to use I fiddled with the original image in Photoshop

An externally hosted image should be here but it was not working when we last tested it.

This can be saved from a right click but has been reduced to 640 px long side, the original is bigger at 890 px
If anyone would like it I can send it by email as a PDF. Please send me a nice message with your email address.

Cheers

 

[Bigun]

Nigel, it does seem that dynamics favour large cones, especially bass. but some say imaging favours smaller cones.

Robin Marshall ex of BBC research inspired my speakers. Pano a moderator here added to it. My first experiments were with conventional drive units and showed that they were hopeless. Sound was glorious but unable to deal with cutting lathe rumble for example. Big paper cone drive units cope very well and show virtually no movement producing surprisingly deep bass. Organ music especially powerful. If you can't hear and feel cutting lathe rumble on 1920s 78s the speakers are not working. Like rock concerts it's unpleasant when the music stops and hum is heard. It is wonderful to hear the room on a 78 with the piano in the background. Very quickly you are almost there and the lack of frequency range is not so obvious. Robin's point to me was that the sound of the Quad electrostatics was not much to do with being electrostatic. He also said magnetic circuits can not be infinitely scaled up unlike amplifiers. Thus higher efficiency is desirable.

The extreme opposite was AR3. Given enough watts they could do a very good job.

 

[nigel pearson]

Absolutely , the Quads and my Magnepans all are compromised this way. I made a remarkable and contradictory discovery. The small DT74/8 tweeter comes in at 6 kHz. It seemed to repair the image width. I used a first order filter so there would have been a hump maybe where it helped

I really liked Robin. I said to him that the BBC LS3/5a needs 500 watts transient. Robin said that's total BS because he had said it. Robin came to the BBC when 3/5a was being researched. Robin said he had to quickly learn and made many of the prototypes. My father's 3/5a are Audiomaster from Robin.

 

[jemraid]

Hello all,

I decided to make mine on Veroboard and have done this layout in MS Publisher

The red links can be reversed for left or right side of the box.
Feel free to copy it, if you would like the original on a PDF or as an MSPub file please send me a nice message

Cheers

 

[nigel pearson]

Bravo. I plan to use RS tag strip. I keep waiting to see what others do. I think I will risk TIP 2955 direct mounted on the anodising with clamp bar.

If only I could have my baffle speakers. If anyone is following that. The best sound I got was on 2 inch polystyrene. I would have made plywood sub baffles to clamp rather than bolts. The outside a wood frame like a window. It was very uncoloured.

 

[jemraid]

Hi Nigel,

Gold plated tag strips Tag boards, tag strips & valve holder boards | Hifi Collective

Blimey!

Cheers

 

[nigel pearson]

I really look forward to it. You are in Rolls Royce land I see. The lady who sold me this house her dad was a senior Concorde stress engineer. He is still alive. Hope he makes it.